FIG. 16 is a cross-sectional view of a conventional capacitor disclosed in JP2004-134632A. Capacitor element 20 has hollow 20A provided therein. A positive electrode and a negative electrode are taken out from both ends of capacitor element 20. Metal case 21 made of aluminum accommodates capacitor element 20 and an electrolyte solution therein. Negative electrode 21A is provided at an outer bottom surface of metal case 21. An end surface of the negative electrode of capacitor element 20 is connected mechanically and electrically to an inner bottom surface of metal case 21 by laser welding while protrusion 21B provided on the inner bottom surface of metal case 21 is put into hollow 20A of capacitor element 20. Sealing plate 22 is made of aluminum. Positive electrode terminal 22A is placed at an outer surface of sealing plate 22. Protrusion 22B is provided on an inner surface of sealing plate 22. Sealing plate 22 has hole 22C for putting the electrolyte solution in the case. The end surface of the positive electrode of capacitor element 20 is connected mechanically and electrically to an inner surface of sealing plate 22 by laser welding. An opening of metal case 21 and sealing plate 22 are sealed with a curling process of curling the opening of metal case 21 with a fringe of sealing plate 22. Pressure regulation valve 23 is attached on an outer surface of sealing plate 22
FIG. 17 is a cross-sectional view of pressure regulation valve 23. Pressure regulation valve 23 includes gas-permeable element 24 closing hole 22C, closing element 25 placed on gas-permeable element 24, and metal cap 26 which covers gas-permeable element 24 and closing element 25 and which is fixed to sealing plate 22. Metal cap 26 has hole 26A for communicating gas-permeable element 24 and closing element 25 with outside. Metal cap 26 urges closing element 25 toward hole 22C so that closing element 25 pushes gas-permeable element 24 to cause gas-permeable element 24 to close hole 22C. Sealing plate 22 has protrusion 22D having an annular shape surrounding hole 22C. Protrusion 22D is deformed by a caulking process to be pressed onto metal cap 26, thereby fixing metal cap 26 to sealing plate 22.
When the pressure of gas in metal case 21 exceeds a predetermined level, pressure regulation valve 23 releases the gas to an outside through hole 22C and 26A, and closes hole 22C again when the pressure falls below the predetermined level, namely the regulation valve is a self-restoring type. Thus, even when gas produced in metal case 21 raises the pressure, no abnormality is caused with an appearance of capacitor 501, and performance of the capacitor remains unchanged.
Gas-permeable element 24 closing hole 22C and intimately pressed onto sealing plate 22 does not permeate the electrolyte solution but permeates the gas produced in metal case 21. Consequently, the electrolyte solution is not attached to closing element 25, thus not damaging pressure regulation valve 23. The electrolyte solution is prevented from leaking through pressure regulation valve 23 to an outside of the capacitor, thus providing capacitor 501 with high reliability.
The end surface of capacitor element 20 of conventional capacitor 501 is welded to the inner surface of sealing plate 22 and the inner bottom surface of metal case 21 with laser radiated from an outside of metal case 21. Consequently, it is difficult to check the welding status and an unnecessary resistance may be increased due to variation in welding condition. A pin hole causing the electrolyte solution to leak may be formed in gas-permeable element 24 or in closing element 25 by sputtering of welding process. In addition, the laser radiated to small areas for welding, accordingly deteriorating reliability in connecting capacitor element 20 to metal case 21 or to sealing plate 22.